universe a few slides collection

1. 28.1 Astronomical distances
 Astronomers have
developed units other
than kilometers or
meters to measure the
vast distances in
space.
 One light year is equal
to the distance that
light travels through
space in one year.

2. 28.1 Determining distances to closer
objects in the universe
 Astronomers use a
method called parallax to
determine the distance of
stars that are closer than
1,000 light years to Earth.
 As Earth revolves around
the Sun, the nearby stars
appear to change
positions in the sky over
the course of one year.

3. 28.1 Determining distances to closer
objects in the universe
 To use parallax,
astronomers determine
the position of a closer
star (moving) in relation to
faraway stars (not
moving).
 Next, they look at the
same star six months
later, and measure its
change in position relative
to the distant stars.

4. 28.1 Studying the universe
 Light from other galaxies
and stars takes time to
reach Earth.
 The farther away the
object they are viewing,
the further back in time
astronomers are looking.

5. 28.1 Telescopes
 Telescopes work by collecting the light
from a distant object with a lens or mirror
and bringing that light into a concentrated
point, called the focal point.

6. 28.1 Telescopes
 A refracting telescope uses lenses to bend, or
refract, light, making objects look bigger.
 Refracting telescopes are made from a long
tube, a glass objective lens that you point
toward the sky, and an eyepiece lens.

7. 28.1 Telescopes
 A reflecting telescope uses
mirrors instead of lenses to
gather and focus light.
 A concave mirror (called the
primary mirror) is placed at
the back of a tube.
 The secondary mirror
deflects the light to an
eyepiece lens.

8. 28.1 Telescopes and electromagnetic
waves
 Astronomers use different types of
telescopes to view the different types of
waves emitted by objects in space.
1. A radio telescope works like an extremely
powerful receiver that picks up radio waves
from space.
2. Infrared telescopes are often placed on
satellites that orbit above Earth.
3. X-ray telescopes are designed to detect
high-energy radiation (X-rays) from space.

9. 28.1 Telescopes and electromagnetic
waves
 These images of the Crab Nebula were taken
with different telescopes.
 Each new view gave astronomers more
information.

10. 28.1 Satellites and other space craft
 The Hubble Space
Telescope is a
satellite that orbits
Earth out of reach of
“light pollution.”
 It sends images from
deep space to
computers back on
Earth.

11. 28.1 Spacecraft
 Space probes are
unmanned spacecraft
that carry scientific
instruments on board.
 Launched in 1977, the
NASA Voyager 1 and 2
probes are still sending
information back to Earth
via radio waves.

12. 28.1 Spacecraft
 Alan Sheppard of the U.S. followed on
May 5.

13. 28.1 Spacecraft
 This led to the
NASA Manned
Lunar Program
known as Apollo,
which lasted from
1963 to 1972.

14. 28.1 Spacecraft
 NASA’s Mars
Exploration Rover
(MER) Mission began
in 2003.
 Two unmanned
rovers, Spirit and
Opportunity, were
sent to explore the
surface features and
geology of Mars. Two generations of Mars Rovers:
Sojourner and Spirit

15. 28.1 Spacecraft
 NASA’s Phoenix
lander launched in
August 2007.
 The lander contains a
robotic arm that digs
through the Martian
soil and brings
samples onboard for
scientific analysis.

16. 28.2 Galaxies
 A galaxy is a huge
group of stars, dust,
gas, and other objects
bound together by
gravitational forces.
 The sun, along with an
estimated 200 billion
other stars, belongs to
the Milky Way galaxy.

17. 28.2 Types of galaxies
 The Milky Way is a flattened, rotating system
that contains young to middle-aged stars,
along with gas and dust.
 Astronomers identify it as a spiral galaxy.

18. 28.2 Types of Galaxies
Astronomers classify galaxies according to
their shape.
1. Spiral galaxies consist of a central, dense
area surrounded by spiraling arms.
2. Barred spiral galaxies have a bar-shaped
structure in the center.
3. Elliptical galaxies look like the central
portion of a spiral galaxy without the arms.
4. Lenticular galaxies are lens-shaped.

19. 28.2 The central black hole theory
 Recent studies have suggested that a black
hole, with a mass of more than a million Suns,
exists at the very center of our galaxy.
 The evidence for a huge black hole comes
from measurements of the orbital velocities of
stars and gas at the center.
 One of the strangest predictions of Einstein’s
theory of relativity is the existence of black
holes.

20. 28.2 The central black hole theory
 The minimum speed an
unpowered projectile
must have to escape the
planet’s gravity is called
the escape velocity.
 A black hole is an object
with such strong gravity
that its escape velocity
equals or exceeds the
speed of light.

21. 28.2 Distances between galaxies
 The distances between stars are 10,000
times greater than the distances between
planets.
 The distances between galaxies are a
million times greater than the distances
between stars.

22. 28.2 Distances between galaxies
 Figuring out the distance between galaxies
is one of the more difficult tasks in
astronomy.
 A faint object in the night sky could be a dim
object that is relatively nearby or a bright
object that is far, far away.

23. 28.2 Distances between galaxies
 The most reliable method
for estimating the distance
to a galaxy is to find a star
whose luminosity is known.
 If the luminosity is known,
the inverse square law can
be used to find the distance
from the observed
brightness.

24. 28.2 Distances between galaxies
 The inverse square law shows how the
brightness of an object decreases as you
move away from it.

25. 28.2 Distances between galaxies
 The inverse square
law is important to
astronomers because
if they know the
brightness and
luminosity of an
object, they can
determine its distance
by rearranging
equation variables.

26. 28.2 Distances between galaxies
 A second type of
standard candle is called
a Cepheid star.
 Cepheid stars “pulsate”
in regular periods
ranging from a few days
to a few weeks.
 By measuring the period
of a Cepheid star,
astronomers determine
its luminosity and then
calculate its distance.

27. 28.3 Doppler Shift
 Doppler shift also
occurs with
electromagnetic
waves, such as
visible light, X-rays,
and microwaves.
 This phenomenon is
an important tool
used by astronomers
to study the motion
of objects in space.

28. 28.3 The expanding universe
 The faster the source
of light is moving
away from the
observer, the greater
the redshift.
 The opposite
(blueshift) happens
when an object is
moving toward the
observer.

29. 28.3 The expanding universe
 Edwin Hubble
discovered that the
farther away a galaxy
was, the faster it was
moving away from
Earth.
 This concept came to
be known as the
expanding universe.

30. 28.3 The Big Bang theory
 The theory that the universe was
expanding implies the universe must have
been smaller in the past than it is today.
 It implies that the universe must have had a
beginning.
 Astronomers today believe the universe
exploded outward from a single point.
 This idea is known as the Big Bang theory.

31. 28.3 The Big Bang theory
 The Big Bang theory says the
universe began as a huge explosion
between 10 billion and 20 billion years
ago.
 According to this theory, all matter
and energy started in a space smaller
than the nucleus of an atom.

32. 28.3 Evidence for the Big Bang theory
 In the 1960s, Arno Penzias
and Robert Wilson were
trying to measure
electromagnetic waves
given off by the Milky
Way.
 The “noise” these
scientists found was the
cosmic microwave
background radiation
predicted by the Big Bang
theory.

33. 28.3 Evidence for the Big Bang theory
 The proportion of hydrogen to helium is
consistent with the physics of the Big Bang.
 If the universe were significantly older, there
would be more heavy elements present
compared with hydrogen and helium.

34. 28.3 Planetary systems
 A star with orbiting planets is called a
planetary system.
 Scientists now believe that planets are a
natural by-product of the formation of stars.

35. 28.3 How the solar system formed
 Scientists think that the solar system was
formed out of the same nebula that created the
Sun.

36. 28.3 Binary stars
 A binary star is a
system with two stars
that are gravitationally
tied and orbit each
other.
 About half of the 60
nearest stars are in
binary (or multiple)
star systems.